Fabrication of a versatile substrate for finding samples on the nanometer scale

With increasing interest in nanometer scale studies, a common research issue is the need to use different analytical systems with a universal substrate to relocate objects on the nanometer scale. Our paper addresses this need. Using the delicate milling capability of a focused ion beam (FIB) system, a region of interest (ROI) on a sample is labelled via a milled reference grid. FIB technology allows for milling and deposition of material at the sub 20-nm level, in a similar user environment as a standard scanning electron microscope (SEM). Presently commercially available transmission electron microscope (TEM) grids have spacings on the order 100 μm on average; this technique can extend this dimension down to the submicrometre level. With a grid on the order of a few micrometres optical, FIBs, TEMs, scanning electron microscopes (SEMs), and atomic force microscopes (AFM) are able to image the ROI, without special chemical processes or conductive coatings required. To demonstrate, Au nanoparticles of ∼ 25 nm in size were placed on a commercial Formvar^®- and carbon-coated TEM grid and later milled with a grid pattern. Demonstration of this technique is also extended to bulk glass substrates for the purpose of sample location. This process is explained and demonstrated using all of the aforementioned analytical techniques.     

Optical microcantilever consisting of channel waveguide for scanning near-field optical microscopy controlled by atomic force

We develop a novel optical microcantilever for scanning near-field optical microscopy controlled by atomic force mode (SNOM/AFM). The optical microcantilever has the bent channel waveguide, the corner of which acts as aperture with a large tip angle. The resonance frequency of the optical microcantilever is 9 kHz, and the spring constant is estimated to be 0.59 N/m. The optical microcantilever can be operated in contact mode of SNOM/AFM and we obtain the optical resolution of about 200 nm, which is as same size as the diameter of aperture. We confirm that the throughput of optical microcantilever with an aperture of 170 nm diameter would be improved to be more than 10⁻⁵.     

Combining AFM and FRET for high resolution fluorescence microscopy

Here we demonstrate a new microscopic method that combines atomic force microscopy (AFM) with fluorescence resonance energy transfer (FRET). This method takes advantage of the strong distance dependence in Förster energy transfer between dyes with the appropriate donor/acceptor properties to couple an optical dimension with conventional AFM. This is achieved by attaching an acceptor dye to the end of an AFM tip and exciting a sample bound donor dye through far-field illumination. Energy transfer from the excited donor to the tip immobilized acceptor dye leads to emission in the red whenever there is sufficient overlap between the two dyes. Because of the highly exponential distance dependence in this process, only those dyes located at the apex of the AFM tip, nearest the sample, interact strongly. This limited and highly specific interaction provides a mechanism for obtaining fluorescence contrast with high spatial resolution. Initial results in which 400 nm resolution is obtained through this AFM/FRET imaging technique are reported. Future modifications in the probe design are discussed to further improve both the fluorescence resolution and imaging capabilities of this new technique.     

Nano-slit probes for near-field optical microscopy fabricated by focused ion beams

The near-field probes described in this paper are based on metallized non-contact atomic force microscope cantilevers made of silicon. For application in high-resolution near-field optical/infrared microscopy, we use aperture probes with the aperture being fabricated by focused ion beams. This technique allows us to create apertures of sub-wavelength dimensions with different geometries. In this paper we present the use of slit-shaped apertures which show a polarization-dependent transmission efficiency and a lateral resolution of < 100 nm at a wavelength of 1064 nm. As a test sample to characterize the near-field probes we investigated gold/palladium structures, deposited on an ultrathin chromium sublayer on a silicon wafer, in constant-height mode.     

Photoconductive imaging in a photon scanning tunnelling microscope capable of point-contact current sensing using a conductive fibre probe

A photoconductive photon scanning tunnelling microscope was developed to investigate the point-contact photoconductive properties of condensed matter. In order to detect the current and the optical signal at a local point on a surface, we coated the edge of a bent type fibre probe with indium tin oxide. Thus it was possible to measure both photocurrent and optical property with subwavelength resolution. The performance of the novel microscope was evaluated by analysing an organic thin film of copper phthalocyanine (CuPc), which is known to be an efficient photoconductive material. Photocurrent and current–voltage characteristics were observed at the local point on the CuPc thin films. Furthermore, photoconductive images were obtained with topography and near-field optical imaging using this system. The photoconductive PSTM shows potential in various areas of future optics and electronics.     

Coaxial probes for scanning near-field microscopy

This paper deals with the development of coaxial aperture tips integrated in a cantilever probe for combined scanning near-field infrared microscopy and scanning force microscopy. A fabrication process is introduced that allows the batch fabrication of hollow metal aperture tips integrated on a silicon cantilever. To achieve the coaxial tip arrangement a metal rod is deposited inside the hollow tip using the focused ion beam technique. Theoretical calculations with a finite integration code were performed to study the transmission characteristics of coaxial tips in comparison with conventional aperture probes. In addition, the influence of the geometrical design parameters of the coaxial probe on its optical behaviour is investigated.     

Imaging of various surface properties of fluorescently labelled phospholipid Langmuir–Blodgett films with a combined scanning probe microscope

We present results of phase separation of a single-component system of 1,2-dihexadecanoyl- sn -glycero-3-phospho-[ N -(4-nitrobenz)-2-oxa-1,3-diazolyl]ethanolamine in which a liquid-condensed (LC) phase co-exists with a liquid-expanded (LE) phase. Domain formation in the co-existence region was studied using a newly developed combined scanning near-field optical microscope–atomic force microscope (SNOM–AFM). We demonstrate for the first time that the topographic, friction, fluorescence and surface potential distributions for a phase-separated single-component Langmuir–Blodgett film between the LE and LC phases can be simultaneously observed using the SNOM–AFM with a thin-step etched optical fibre probe.     

Evaluation of fracture planes and cell morphology in complementary fractures of cultured cells in the frozen-hydrated state by field-emission secondary electron microscopy: feasibility for ion localization and fluorescence imaging studies

We have employed field-emission secondary electron microscopy (FESEM) for morphological evaluation of freeze-fractured frozen-hydrated renal epithelial LLC-PK₁ cells prepared with our simple cryogenic sandwich-fracture method that does not require any high-vacuum freeze-fracture instrumentation (Chandra et al. (1986) J. Microsc. 144 , 15–37). The cells fractured on the substrate side of the sandwich were matched one-to-one with their corresponding complementary fractured faces on the other side of the sandwich. The FESEM analysis of the frozen-hydrated cells revealed three types of fracture: (i) apical membrane fracture that produces groups of cells together on the substrate fractured at the ectoplasmic face of the plasma membrane; (ii) basal membrane fracture that produces basal plasma membrane-halves on the substrate; and (iii) cross-fracture that passes randomly through the cells. The ectoplasmic face (E-face) and protoplasmic face (P-face) of the membrane were recognized based on the density of intramembranous particles. Feasibility of fractured cells was shown for intracellular ion localization with ion microscopy, and fluorescence imaging with laser scanning confocal microscopy. Ion microscopy imaging of freeze-dried cells fractured at the apical membrane revealed well-preserved intracellular ionic composition of even the most diffusible ions (total concentrations of K⁺, Na⁺ and Ca⁺). Structurally damaged cells revealed lower K⁺ and higher Na⁺ and Ca⁺ contents than in well-preserved cells. Frozen-freeze-dried cells also allowed imaging of fluorescently labelled mitochondria with a laser scanning confocal microscope. Since these cells are prepared without washing away the nutrient medium or using any chemical pretreatment to affect their native chemical and structural makeup, the characterization of fracture faces introduces ideal sample types for chemical and morphological studies with ion and electron microscopes and other techniques such as laser scanning confocal microscopy, atomic force microscopy and near-field scanning optical microscopy.     

High-speed scanning by dual feedback control in SNOM/AFM

We have developed a high-speed scanning near-field optical microscope (SNOM)/atomic force microscope (AFM) system including dual feedback controllers. The system includes an additional piezoelectric actuator with fast response in the z direction and a correction circuit to eliminate unnecessary components from the feedback signal. From the measurement of a patterned chromium layer of 2 × 2 μm² checks on a quartz glass plate, we confirmed that our system had more effective feedback control and faster scanning than current SNOM/AFM systems that use only a piezo-tube. The scanning speed of the present system was estimated to be about five times faster than that of current SNOM/AFM systems.     

悬臂式光纤探针

悬臂式探针的研制是 SNOM- AFM的重要技术之一。用熔拉—腐蚀相结合的方法 ,将普通单模石英光纤制成直锥型探针。再利用自制的工具在 CO2 激光束下将针尖打弯 ,制成悬臂式探针样品。简单地讨论了此种探针的弹性常数     

High-Resolution Lithography with Near-Field Optical Microscopy

Scanning near-field optical microscopy (SNOM) is used for lithography to avoid the resolution limiting diffraction of conventional optical methods. We have expanded a commercial SNOM for writing even complex structures on the nanometer scale. Scanning near-field optical lithography (SNOL) has been applied to conventional resists to explore its potential and the possible combination with conventional optical lithography (mix and match technique).     

原子力显微镜在DNA研究中的应用

原子力显微镜作为一种新型的表面表征手段已经得到了各个方面的应用，本文探索了AFM在DNA表面结构中的研究方法，讨论了AFM在研究DNA中优势。     

High-resolution constant-height imaging with apertured silicon cantilever probes

We present high-resolution aperture probes based on non-contact silicon atomic force microscopy (AFM) cantilevers for simultaneous AFM and near-infrared scanning near-field optical microscopy (SNOM). For use in near-field optical microscopy, conventional AFM cantilevers are modified by covering their tip side with an opaque aluminium layer. To fabricate an aperture, this metal layer is opened at the end of the polyhedral probe using focused ion beams (FIB). Here we show that apertures of less than 50 nm can be obtained using this technique, which actually yield a resolution of about 50 nm, corresponding to λ/20 at the wavelength used. To exclude artefacts induced by distance control, we work in constant-height mode. Our attention is particularly focused on the distance dependence of resolution and to the influence of slight cantilever bending on the optical images when scanning at such low scan heights, where first small attractive forces exerted on the cantilever become detectable.     

Femtosecond near-field scanning optical microscopy study of molecular thin films

A near-field scanning optical microscope has been combined with a two-colour time-resolved pump-probe measurement system. It has a noise-equivalent transmittance change of 5.0 × 10⁻⁵ for a probe pulse with an intensity of 30 nW. The system has been used for evaluating molecular thin films that have a domain structure, particularly for observing a gate action of the single domains. The results include key features to understand an origin of the domains and suggest that the film composition is uniform over a distance of several micrometres.